test(config): cover EnvRegistry and EnvironmentConfig overrides

Add unit tests for the runtime-override mechanism that previously shipped
untested: EnvRegistry string/stringOrNull/boolean/integer (override-wins,
empty-as-unset, malformed-fallback), has/clear, and EnvironmentConfig
applyOverrides/clearOverrides incl. the non-positive polling-interval guard.

Author: SERDUN

test/environment_config_test.dart

@@ -0,0 +1,95 @@
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:webtrit_phone/environment_config.dart';
+
+void main() {
+  group('EnvRegistry', () {
+    late EnvRegistry registry;
+
+    setUp(() => registry = EnvRegistry());
+
+    test('string: override wins; empty and missing fall back to compile-time', () {
+      registry.apply({'A': 'override'});
+      expect(registry.string('A', 'default'), 'override');
+
+      registry.apply({'A': ''});
+      expect(registry.string('A', 'default'), 'default');
+
+      registry.apply({});
+      expect(registry.string('A', 'default'), 'default');
+    });
+
+    test('stringOrNull: empty and missing fall back (may be null)', () {
+      registry.apply({'A': ''});
+      expect(registry.stringOrNull('A', null), isNull);
+      expect(registry.stringOrNull('A', 'd'), 'd');
+
+      registry.apply({'A': 'x'});
+      expect(registry.stringOrNull('A', 'd'), 'x');
+    });
+
+    test('boolean: true/false honoured; malformed and empty fall back', () {
+      registry.apply({'B': 'TRUE'});
+      expect(registry.boolean('B', false), isTrue);
+
+      registry.apply({'B': 'false'});
+      expect(registry.boolean('B', true), isFalse);
+
+      registry.apply({'B': 'yes'}); // malformed -> compile-time
+      expect(registry.boolean('B', true), isTrue);
+
+      registry.apply({'B': ''}); // empty -> compile-time
+      expect(registry.boolean('B', true), isTrue);
+
+      registry.apply({});
+      expect(registry.boolean('B', false), isFalse);
+    });
+
+    test('integer: numeric honoured; malformed and empty fall back', () {
+      registry.apply({'N': '42'});
+      expect(registry.integer('N', 1), 42);
+
+      registry.apply({'N': 'abc'});
+      expect(registry.integer('N', 7), 7);
+
+      registry.apply({'N': ''});
+      expect(registry.integer('N', 7), 7);
+    });
+
+    test('has / clear', () {
+      registry.apply({'A': 'x'});
+      expect(registry.has('A'), isTrue);
+
+      registry.clear();
+      expect(registry.has('A'), isFalse);
+    });
+  });
+
+  group('EnvironmentConfig overrides', () {
+    tearDown(EnvironmentConfig.clearOverrides);
+
+    test('APP_NAME reflects an override and falls back when empty/cleared', () {
+      EnvironmentConfig.applyOverrides({EnvironmentConfig.APP_NAME__NAME: 'Custom'});
+      expect(EnvironmentConfig.APP_NAME, 'Custom');
+
+      EnvironmentConfig.applyOverrides({EnvironmentConfig.APP_NAME__NAME: ''});
+      expect(EnvironmentConfig.APP_NAME, 'WebTrit');
+
+      EnvironmentConfig.clearOverrides();
+      expect(EnvironmentConfig.APP_NAME, 'WebTrit');
+    });
+
+    test('a non-positive polling-interval override falls back to the default', () {
+      const name = EnvironmentConfig.USER_REPOSITORY_POLLING_INTERVAL_SECONDS__NAME;
+
+      EnvironmentConfig.applyOverrides({name: '0'});
+      expect(EnvironmentConfig.USER_REPOSITORY_POLLING_INTERVAL_SECONDS, 10);
+
+      EnvironmentConfig.applyOverrides({name: '-5'});
+      expect(EnvironmentConfig.USER_REPOSITORY_POLLING_INTERVAL_SECONDS, 10);
+
+      EnvironmentConfig.applyOverrides({name: '30'});
+      expect(EnvironmentConfig.USER_REPOSITORY_POLLING_INTERVAL_SECONDS, 30);
+    });
+  });
+}